1. Field of the Invention
The present invention relates to a storage device such such as FDD, HDD, CD-ROM, and the like.
2. Description of the Prior Art
A storage device of this type is constituted by a chassis attached with or housing constituent components of the device, a spindle motor for rotating information recording disks, magnetic heads for reading/writing information in/from the information recording disks, an actuator for driving these magnetic heads in the radial direction of the information recording disks, and a control circuit for controlling the operation of the whole device. As the spindle motor, which requires the highest cost and precision of all the constituent components, a three-phase brushless DC motor has conventionally been used due to high performance requirements.
However, the three-phase brushless DC motor cannot cope with demands for further cost reductions in recent years, so a lower-cost motor is required. When a claw-pole two-phase synchronous motor is considered in the light of this problem, since this motor is basically a stepping motor, its shaft speed greatly varies, and its rotating shaft vertically fluctuates depending on the state of magnetic excitation. For this reason, the claw-pole two-phase synchronous motor fails to attain smooth rotation required for a spindle motor, and it cannot provide satisfactory effects. In addition, a motor drive excitation coil functions like a solenoid coil due to its specific motor arrangement so that a large leakage magnetic flux is generated on every excitation and the leaked flux links to the magnetic head, resulting in a low S/N ratio of the head output signal.